#box1 {
    width: 100px;
    height: 100px;
    background-image: url("./aa.ico");
    background-size: 100% 100%;
}

#box2 {
    width: 100px;
    height: 100px;
    background-image: url("./bb.png");
    background-size: 100% 100%;
}

#box3 {
    width: 100px;
    height: 100px;
    background-image: url("./cc.svg");
    background-size: 100% 100%;
}